[dm-devel] Re: Too many I/O controller patches

[Andrea Righi <righi andrea gmail com>]

Hirokazu Takahashi wrote:
> Hi, Andrea,
>
> I'm working with Ryo on dm-ioband and other stuff.
>
> > > On Mon, 2008-08-04 at 20:22 +0200, Andrea Righi wrote:
> > > > But I'm not yet convinced that limiting the IO writes at the device
> > > > mapper layer is the best solution. IMHO it would be better to throttle
> > > > applications' writes when they're dirtying pages in the page cache (the
> > > > io-throttle way), because when the IO requests arrive to the device
> > > > mapper it's too late (we would only have a lot of dirty pages that are
> > > > waiting to be flushed to the limited block devices, and maybe this could
> > > > lead to OOM conditions). IOW dm-ioband is doing this at the wrong level
> > > > (at least for my requirements). Ryo, correct me if I'm wrong or if I've
> > > > not understood the dm-ioband approach.
> > > The avoid-lots-of-page-dirtying problem sounds like a hard one.  But, if
> > > you look at this in combination with the memory controller, they would
> > > make a great team.
> > >
> > > The memory controller keeps you from dirtying more than your limit of
> > > pages (and pinning too much memory) even if the dm layer is doing the
> > > throttling and itself can't throttle the memory usage.
> > mmh... but in this way we would just move the OOM inside the cgroup,
> > that is a nice improvement, but the main problem is not resolved...
>
> The concept of dm-ioband includes it should be used with cgroup memory
> controller as well as the bio cgroup. The memory controller is supposed
> to control memory allocation and dirty-page ratio inside each cgroup.
>
> Some guys of cgroup memory controller team just started to implement
> the latter mechanism. They try to make each cgroup have a threshold
> to limit the number of dirty pages in the group.

Interesting, they also post a patch or RFC?

-Andrea